1. Technical Field
The present invention relates to a pulse generator, a communication device and a pulse generation method which are applied to, for example, a wireless communication system using a pulse.
2. Related Art
Recently, wireless terminal devices such as a mobile phone and a wireless LAN have grown dramatically in popularity, and a frequency band used in communication therein has also extended to a GHz band. For this reason, there is a situation in which it is difficult to use a new frequency band for communication.
Under this kind of situation, a communication method using an impulse-like pulse and whose width is very narrow (for example, around 1 ns), has drawn attention as a new method of using frequency resources.
As this kind of communication method using the pulse, for example, a communication method described in JP-A-10-508725 (Abstract and FIG. 10) (hereafter referred to as Patent Document 1) has been proposed. In this communication method using the pulse, unlike a signal transmission using a normal continuous wave, an information transmission is carried out by means of an intermittent energy transmission and reception. This kind of communication method using the pulse, being of low power consumption and likely to achieve a miniaturization of the device, is suitable for a mobile device such as the mobile phone.
Also, the width of the pulse used to bear the information transmitted by means of the communication method using the pulse is very narrow, as heretofore described, and consequently, a frequency band of a frequency spectrum of the pulse becomes wider than in communication using the normal continuous wave, dispersing a signal energy.
As a result thereof, a signal energy per unit frequency band is minimized, there is less fear of causing interference with another communication system, and a sharing of the frequency band is taken to be possible.
However, a case in which another communication system is in proximity is not limited to this. For example, in a kind of case in which a communication system using the pulse and the other communication system are mixed in an identical casing of an electronic device, it may happen that communication between two-way devices in the communication system using the pulse exerts interference on the other communication system. In the same way, it may happen that the communication suffers interference from the other communication system.
Focusing attention on the heretofore described problem, a proposition for minimizing an interference signal directed to another device has also been made, for example, as shown in JP-A-2004-336764 (Paragraphs 0006 to 0013) (hereafter referred to as Patent Document 2).
That is, a technology of, in order to minimize power while guaranteeing a communication quality to some extent, detecting a signal-to-noise ratio (SNR) or a bit error rate (BER), and changing a coding rate, a modulation order (BPSK, QPSK), a pulse interval (a clock speed) or transmission power, is disclosed in Patent Document 2.
However, although the technology disclosed in Patent Document 2 is one which adapts a technique, which is also applied to a heretofore known wireless communication method which makes the coding rate, modulation order (BPSK, QPSK) or clock speed variable, to the communication using the pulse, in practice, it being insufficient as a measure against an interference wave in communication using a pulse having a very wide bandwidth, a possibility of a band used for that communication system extending into a band used by another communication cannot be eliminated.